AP Style Meridians

Use numerals and lowercase to identify the imaginary locater lines that ring the globe from north to south through the poles.

They are measured in units of 0 to 180 degrees east and west of the “prime meridian,” which runs through Greenwich, England.

Here are some examples,

• 33^rd meridian (if location east west of Greenwich is obvious)
• 1^st meridian west
• 100^th meridian

See also AP Style Latitude and Longitude